The goal of this project is to understand the mechanisms by which templated nucleotide polymerizing enzymes achieve fidelity. Previous workers have concentrated on the 3' yields 5' exonuclease associated with many DNA polymerases, analyzing the role that this activity plays in proofreading the results of the polymerizing step. However, the mechanism by which the polymerizing step achieves accuracy has been largely ignored. To investigate the latter I intend to examine the effect of polymerase substrate analogues on the fidelity of the polymerization reaction. Nucleotide triphosphates modifed in the phosphate moieties (either the beta or gamma position or both) will be utilized with the view that decreased rate of polymerization is likely to manifest itself as a decrease in the fidelity of polymerization. Both misincorporations and indirect changes effected by altered fidelity at the polymerization step will be analyzed. (Note that by only altering the beta and gamma positions, there should be no effect of the modification once the beta-gamma pyrophosphate bond has been hydrolyzed, e.g., no affect on the 3' yields 5' exonuclease).